The disclosure of Japanese Patent Application No. 2001-180657 filed on Jun. 14, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an oil pump control device and method for an automatic transmission. In particular, the invention relates to a control device for an electric oil pump disposed in an automatic stop/restart-type engine vehicle in which an engine is stopped automatically upon fulfillment of one of a predetermined number of running conditions of the vehicle, namely, a so-called economy-running vehicle.
2. Description of Related Art
A vehicle having an engine that is stopped automatically upon fulfillment of one of a predetermined number of running conditions of the vehicle and that is restarted automatically for takeoff by a certain operation performed by a driver, such as a depression of an accelerator pedal, has been known for a long time as a so-called economy-running vehicle. In the case where an automatic transmission is adopted in such an automatic stop/restart-type engine vehicle, a mechanical oil pump driven by an engine ensures a hydraulic pressure for operating a friction coupling element and a change-gear mechanism in the automatic transmission. If the engine is stopped automatically upon fulfillment of one of a predetermined number of running conditions of the vehicle, the mechanical oil pump driven by the engine is stopped as well. For this reason it becomes impossible to ensure a hydraulic pressure for operating the friction coupling element and the change-gear mechanism in the automatic transmission when the engine is restarted. In quest of a solution to this problem, Japanese Patent Application Laid-Open No. 10-324177 discloses the idea of additionally providing an electric oil pump that is electrically driven to supply an automatic transmission with a hydraulic pressure.
FIG. 5 is an exemplary diagram showing how an electric oil pump is arranged in relation to the other component members of a so-called economy-running vehicle according to the related art. An output torque of an engine 1 is input to an automatic transmission 3 via a torque converter 2 and output to an output shaft 4 of the vehicle. An electric oil pump 6 is disposed in parallel with a mechanical oil pump 5 driven by the engine 1. An output from the electric oil pump 6 is coupled with an output from the mechanical oil pump 5 via a check valve 7 and then transmitted to the automatic transmission 3. The electric oil pump 6 is supplied with electric power from a battery 8 via a driver circuit 9, which is connected to an oil pump control device 10.
It will now be described how the construction described above operates. When the engine 1 is running, an output torque of the engine 1 is output to the output shaft 4 via the torque converter 2 and the automatic transmission 3 and drives the mechanical oil pump 5 at the same time. A hydraulic pressure generated at this moment is transmitted through a hydraulic circuit and suitably controlled by hydraulic pressure control device (not shown). The hydraulic pressure thus controlled is supplied to the automatic transmission 3. On the other hand, if the engine 1 is stopped automatically and enters an economy-running state, the mechanical oil pump 5 stops operating and no longer generates a hydraulic pressure. In this case, the oil pump control device 10 transmits a drive signal for controlling an operation of the electric oil pump 6 to the driver circuit 9, and electric power in the battery 8 is then supplied to the electric oil pump 6 via the driver circuit 9, whereby the electric oil pump 6 is operated and generates a hydraulic pressure. This hydraulic pressure is transmitted through the hydraulic circuit via the check valve 7, suitably controlled by the hydraulic pressure control device (not shown), and supplied to the automatic transmission 3. The check valve 7 prevents a high hydraulic pressure in the mechanical oil pump 5 from being transmitted reversely to the electric oil pump 6.
As described hereto, it is not the mechanical oil pump 5 but the electric oil pump 6 that operates when the engine 1 is out of operation. The electric oil pump 6 thus ensures a hydraulic pressure for operating the change-gear mechanism and the friction coupling element. As a result, the engine 1 can be restarted appropriately.
In the aforementioned related art, the electric oil pump is in operation when the mechanical oil pump is out of operation during stoppage of the engine. The electric oil pump generates a hydraulic pressure which ensures operation of the friction coupling element and the change-gear mechanism, whereby the engine can be restarted appropriately. However, the hydraulic pressure output from the electric oil pump must be set much higher than an optimal output hydraulic pressure, in consideration of differences or aging-based changes in the performance of a motor for driving the electric oil pump, the output voltage of the driver circuit, the clearance of valves disposed in the automatic transmission or the hydraulic pressure controller thereof, and the like. For this reason, problems such as a shortened period of endurance of the motor and a deterioration in fuel consumption resulting from an increase in power consumption in an economy-running state are caused. A solution to these problems requires controlling the output hydraulic pressure on the basis of a result obtained by monitoring the optimal output hydraulic pressure. However, it is not appropriate to merely monitor the hydraulic pressure in the electric oil pump. That is, the output hydraulic pressure needs to be controlled on the basis of a result obtained by monitoring the optimal output hydraulic pressure in such a manner that a shock occurring in the change-gear mechanism during the coupling of the friction coupling element, such as the axle clutch, does no harm to the driveability of the vehicle.
The invention thus provides an oil pump control device for an automatic transmission which offers an adequate solution to the problems caused in the control device for the electric oil pump according to the related art and which ensures an optimal hydraulic pressure output from the electric oil pump from the standpoint of operating a friction coupling element and a change-gear mechanism.
In order to achieve the objective stated above, an oil pump control device for an automatic transmission according to one aspect of the invention comprises an electric oil pump that is electrically driven to supply the automatic transmission with a hydraulic pressure, and a controller that updates the hydraulic pressure generated by the electric oil pump on the basis of kinetic characteristics of a torque transmission system during a start of an engine that is stopped automatically upon fulfillment of one of a predetermined number of running conditions of a vehicle and optimizing a hydraulic pressure supplied to the automatic transmission during a restart of the engine.
A control method of the oil pump control device comprises the steps of setting a driving pattern of a motor for an electric oil pump that supplies a hydraulic pressure to an automatic transmission, measuring an input speed of the automatic transmission, and correcting the driving pattern on the basis of the input speed and a hydraulic pressure in the electric oil pump.